The requirements for antigen recognition by T cells remain elusive. In this investigation, the requirements for stimulation of and target lysis by cytotoxic T lymphocytes (CTL) will be examined by using purified H-2 antigens incorporated into liposomes for in vitro CTL assays. Also, attention will focus on the possible role of beta-2-microglobulin in recognition of target antigens by CTL. The goal here is to begin dissecting CTL recognition events at the molecular level in order to better understand the constraints antigen imposes on CTL during their activation and actions.